1. Field of the Invention
The present invention relates to a contact heating device for heating an object to be heated in contact therewith such as a die bonding heater or the like used when a semiconductor bare chip is mounted on a substrate.
2. Prior Art
As a packaging method for mounting a semiconductor bare chip on a circuit substrate, the ACF bonding method is known, by which pad electrodes on a chip and those on a substrate are bonded by using a resin-based adhesive such as an anisotropic conductive film or the like. As another mounting method, the flip chip bonding method, by which pad electrodes on a chip and those on a substrate are bonded by using low melting braze material such as Auxe2x80x94Si, Auxe2x80x94Sn alloys or the like, is also utilized for manufacturing multiple chip modules.
As shown in FIG. 5A, in the flip chip bonding method, a semiconductor chip 8 is placed on a multi-layered substrate 85, a pressing tool 910 fixedly bonded to a bonding heater 92 is brought into contact with an upper surface of the chip 8 and then the chip is pressed while heated. The semiconductor chip 8 is brazed on the substrate 85 by melting solders 82, 87 between pad electrodes 81, 86. After cooling, bonding of the pad electrodes 81, 86 and wiring are completed and the semiconductor chip 8 is fixed on the substrate 85. After this operation, the pressing tool 910 is separated from the semiconductor chip 8 and moved to another semiconductor chip 8. The pressing tool 910 captures the chip to carry out the same bonding operation.
As characteristics of a bonding heater 92, firstly, it is required to efficiently transfer necessary and sufficient heat to the bond material via a semiconductor chip 8 in order to soften or melt bond material such as solders 82, 87 used for bonding of bump electrodes or the like.
Secondly, from the viewpoint of production efficiency, it is important that time for a temperature rise to a required temperature and time for a temperature fall after bonding until the bond material is solidified are both short.
Thirdly, since pressure as well as heat is applied when a semiconductor chip 8 is bonded, the bonding heater 92 and tool 910 are required to have mechanical strength and abrasion resistance.
To achieve these performances, the bonding heater 92 is constituted by a sintered body composed of a small amount of heat-resistant metal such as titanium, molybdenum or the like as a sintering additive and diamond particles (for example, a diamond sintered body, as disclosed in Japanese Patent Laid-Open Publication No. 11-240762) and utilized as a tool 910. This is a pulse heater method, in which large pulse current is allowed to flow in the heat-resistant metal itself such as titanium, molybdenum or the like contained in the tool in order to heat the tool.
Japanese Patent Laid-Open Publication No. 10-134938 discloses a bonding heater shown in FIG. 5B. The heater is composed of a ceramic head 91 (or tool) and a ceramic holder 94 for connecting the head 91 to another member. Here, a thermal conductivity of the head 91 is made higher than that of the holder 94. The head 91 is fixedly bonded to a ceramic heater 92 by using a high melting point glass bonding layer 911. Glass material of this bonding layer 911 has a composition consisting of a combination of any selecting from silicon nitride, aluminum nitride, alumina, silicon oxide, zirconia, alkaline-earth metal oxide and rare-earth element oxide and has a high melting point of 1500-1800xc2x0 C.
To accelerate a temperature fall, in Japanese Patent Laid-Open Publication No. 11-339929, use of a water cooling jacket is proposed to improve a temperature fall speed which is slow due to cooling by standing. As shown in FIG. 6, the water cooling jacket 96 is embedded in a holder body 95 and forcibly cools the holder 94, thereby indirectly cooling the bonding heater 92 and tool 91 provided to the heater holder 94.
While, microcomputers requiring a small size, high density and high speed processing such as a portable telephone, mobile computer and the like are rapidly being further widespread, higher performances are being achieved. Under these circumstances, more highly integrated semiconductor chip packaging and miniaturization are further required. Along with this, semiconductor chips have a more variety of sizes and arc required to be mounted on multi-layered packaging substrates.
In the conventional bonding heater as shown in an example in FIG. 5A, as described above, a bonding heater 92 and tool 910 are integrally bonded to each other. In an example in FIG. 5B as well, a ceramic heater 92 and a head 91 are completely bonded by a bonding material 911. Therefore, such conventional bonding heaters are not adaptable to chips having different chip sizes. In addition, even if only either the tool 91 and 910 or bonding heater 92 is damaged, both of these need to be replaced.
In the bonding heater 92, the tool 91 and 910 needs to have a uniform surface temperature over tho surface area in order to uniformly bond pad electrodes on the whole surface of a semiconductor chip 8. However, the conventional bonding heater 92 has a disadvantage that the temperature of a peripheral portion of the tool 91 and 910 lowers due to heat dissipation into air.
Since location accuracy of mounting or the like in semiconductor chip packaging significantly affects performances of electronic equipment, deformation of the contact heating device itself due to thermal expansion is also a problem. When the contact heating device employs a pulse heater method, large current pulses are applied to a resistor composed of titanium or molybdenum for a rapid temperature rise. As a result, the heater itself is vibrated and the actually mounted position is displaced from the position where the semiconductor chip 8 is originally located. This displacement significantly affects performances of the electronic equipment on which the semiconductor chip is mounted.
On the other hand, in a constant heater method, in which the heater is continuously used, when the heater is used at a temperature of 500xc2x0 C., the temperature of the holder 94 rises to 100-150xc2x0 C. However, since the holder 94 is composed of metallic material, a warpage occurs due to a temperature distribution generated in the holder 94. Consequently, accuracy of semiconductor chip mounting location is deteriorated.
The bonding heater 92 is also required to speed up a temperature rise and temperature fall to shorten the work tact. In particular, in the above flip chip process, the temperature needs to be rapidly increased to a prescribed temperature to soften the bond material and position the semiconductor chip 8. However, it takes a long time to heat up the bonding heater 6 using heat-resistant metal such as titanium, molybdenum or the like to a prescribed temperature.
Furthermore, the bonding heater 92 is required to shorten time required for cooling to shorten the work tact. For example, time for a use temperature fall from 400xc2x0 C. to 100xc2x0 C. needs to be 10 seconds or less. However, in the bonding heater 92 using heat-resistant metal such as titanium, molybdenum or the like, time required to cooling, for example, from 400xc2x0 C. to 100xc2x0 C. is 20 seconds or longer even if a water cooling jacket 96 is used as shown in FIG. 6.
Accordingly, an object of the present invention is to provide a contact heating device which can be assembled so that each element can be individually replaced if either a ceramic heater or tool is damaged.
Another object of the present invention is to provide a contact heating device capable of making a temperature of a tool contact surface uniform.
Another object of the present invention is to provide a contact heating device which does not vibrate so that a semiconductor chip is not displaced and precisely positioned during soldering operation.
Another object of the present invention is to provide a contact heating device capable of being rapidly heated to a prescribed temperature to shorten heating time.
Another object of the present invention is to provide a contact heating device further capable of being rapidly cooled after heated to shorten cooling time.
A contact heating device of the present invention is constituted by a ceramic tool for pressing an object to be heated, a ceramic heater for heating the tool, a heat insulating member for transferring heat generated by the ceramic heater mainly to the tool side and a holder for integrating these members and connecting these members to another member and is characterized in that the tool, ceramic heater, heat insulating member and holder are detachably bonded.
The present invention can provide a contact heating device which can bond semiconductor chips in various sizes by detachably bonding the tool, ceramic heater, heat insulating member and holder and can be easily maintained even if a ceramic heater or tool portion in use is damaged.
In the present invention, the tool is preferably fixed by vacuum suction by the ceramic heater to make each element detachable. On the other hand, the ceramic heater can be threadedly fixed to the heat insulating member and the heat insulating member is threadedly fixed to the holder.
As such vacuum suction means, a ring groove is formed in the ceramic heater surface and communicated to first suction through holes which are disposed penetratingly through the heat insulating member. A second suction through hole can also be disposed which opens in the tool surface and penetrates through the tool, ceramic heater, heat insulating member and holder.
In the contact heating device of the present invention, a heat insulating member and/or holder is provided with a coolant path. so that a coolant is allowed to flow at the time of cooling the ceramic heater in order to directly cool the heater quickly, thereby achieving a rapid temperature fall. Furthermore, since a temperature rise is suppressed by cooling the heat insulating member and holder, thermal deformation of the heat insulating member and holder is made extremely small to decrease packaging accuracy of the chip on the substrate.
As such cooling means, a cooling path allowing a coolant to flow in the heat insulating member and/or holder can be provided. A groove in which the coolant is allowed to flow may be formed in the bonding surface of the ceramic heater and heat insulating member, and at least one cooling hole communicated with the groove can also be penetratingly formed through the heat insulating member to accelerate cooling of the ceramic heater. A groove may also be formed in the bonding surface of the holder so that the grooves is communicated with a cooling hole which is penetratingly formed in the holder to cool the holder.
It is preferable that a thermal conductivity of the tool is 100 W/mxc2x7K or higher and that the thermal conductivity of the ceramic heater is 10 W/mxc2x7K or higher. On the other hand, a thermal conductivity of the heat insulating member is preferably made 5 W/mxc2x7K or lower to achieve a uniform temperature of the tool surface and rapid heating.
The tool, ceramic heater, heat insulating member and holder preferably have a thermal expansion coefficient of 6xc3x9710xe2x88x926/K or lower in order to prevent thermal deformation.